Pressing mold for the manufacture of briquettes from fine-grained materials in powder form and the like



Sept. 14, 1937. w, BOLK 2,09

PRESSING MOLD FOR THE MANUFACTURE OF BRIQUETTES FROM FINE GRAINED MATERIALS IN POWDER FORM AND THE LIKE Filed May 8, 1935 UNITED STATES PAT-E Patented Sept. 14, 1937 PnEssINc Mow FOR THE, MANUFACTURE or anroosr'rss' FRoM FINE-GRAINED MATERIALS IN POWDER FORM AND THE HKE h Willem Bolk, Arnhem, Netherlands, assignor to Naamlooze Vennootschap Maatschappij tot Exploitatie van ten-Bosch Octrooien N. V., Arnhem, Netherlands, a corpo ration of the NT oFFicE Netherlands Application May 8, 1935, SerialNo. 20,500

In Germany March.5,1935

1 Claim. (01.? 18-534) 10 It is to be borne in mind, however, that there is a difference between the state of tension which exists during the compressing action, 1. e. during,

the period in which the pressure to be exerted on the mass to be compressed is being raised from 15 atmospheric pressure to maximum pressure, and

the state of tension existing during relief of pressure, i. e. during the period extending from the attainment of the maximum pressure to the moment at which the pressure is reduced to at- 20 mospheric.

If a substance, such as, coal dust, blast furnace dust or petroleum coke, is compressed from all directions and the pressure components each of which is acting on a unit of the briquette surface 2 are continually kept equal-and the pressure is then relieved while also keeping equal the pres-' sure components acting'on each unit of the bri quette surface, the formation of fissures i 'the' briquette will be prevented.

3 By this method of compressing, the briquette thus formed will become isotropic which means that the elastic properties of the briquette will be at all times equal in all directions. r

For carrying out this method of pressing and relieving the pressure very complicated presses are however, required Such presses are of the type in which the compression chamber is enclosed by a number of compression plates, each of which is separately movable.

40 'My invention now has for its purpose to obtain the desired results with a considerably simplified construction of the presses required- As, aspecific form of mold for practising the method according-to the present invention, a. matrix, the

5 generatrix of which satisfies the equation,

In solving this problem I have started fromthe principlethat .it 'ispermissible to deviate from 55 the requirement to. keepthexbriquette continuously in a homogeneous state of tension, as it has been ascertained that-deviations within certain-limits of the homogeneous stateof tension may be tolerated. I

' My invention which will be further described hereinafter'is based -on the following considerations: H a In the equations found herebelow the symbols used are as follows:

1g=logarithm e= elongation per unit of length ,er=radia1 elongation per unit of length Ea axial elongation-per unit of length a: tangential elongation per unit of length 07 tension (indicated at the end of the arrow normal to, the long side in Fig. 2)

a: radial tension m=axial tension at=tangential tension E=modulus of elasticity m=coefficient of contraction -r=shearing stress angle "between tangent at point and X axis (see Fig. 1).

If a substance is compressed in a cylindrical matrix or-press die between two axial rams, it can-be ascertained that the resulting briquette isnot isotropic- (the elastic properties being un-' equal in all directions). It appears that when relieving the pressure the expansion in the direction of compression (axial direction) exceeds that in a direction perpendicular thereto (radial direction). During the pressing in one direction, a departure from the homogeneous condition of tension occurs insuch a manner that, axially, larger pressures are producedthan radially. Dur ing the compression, however, the departure from the homogeneous condition of tension is of secondary importance. When the compression rams are retracted then the axial pressure decreases in a higher degree than the radial pressure; "'I'h'ere however,- a moment, at which the condition of tension, apart from, thefriction along the Walls, is again homogeneousf If, however, the compression rams are furtherretracted, then the axial pressure willdrop beneath the. radial pressure andthen a departure from the homogeneous con-, dition of tension occurs again. In order to prevent a breaking 2up-of thebriquette said departure should be suitably limited. This can be ob;- tained by using a matrix, in which according to the invention the interior wall of the mold is formed by the bounding surface of a solid 01.

revolution, the generatrix of which surface satisfies the equation:

with respect to a coordinate system, the y-axis of which coincides with the axis of rotation.

The invention will be further explained with the aid of the drawing in which Fig. 1 represents a perspective view, partly in section of a pressing mold or matrix according to the invention.

Fig. 2 represents a particle of the material belonging to the outer surface of the briquette, the forces acting on the same being indicated by arrows.

Assuming now that a substance is contained in a cylindrical compression-space denoted by a dotted line I in Fig. 1 under a bi-axial (X- and Z-axes) homogeneous condition of tension, while on said substance a specific surface pressure p is exertedin axial direction and a specific surface pressure q in radial direction, then in any point of the cylinder the same conditions of tension and deformation will occur, which are characterized by the radial, tangential and axial tensions dr=q; n=q; 04:17 and the corresponding specific strains er; et=er and EG- If a pressure is exerted on a cylinder in an axial direction only, it will be obvious that the tensions occurring in across section of this cylinder, perpendicular to the axis will all be equal, so that indeed under these circumstances it also may be said that the radial and tangential tensions are equal.

The tension and deformation value in the case of a homogeneous and isotropic substance are correlated as follows:

The requirement now is to so determine the meridian curve 2 that in the caseof a deformation of the part bounded by said meridian curve under the load .2), q each point of the curve 2 again reaches said curve. I

The point 330, gm after deformation will lie at $1=(1+er)$o Z11: (1+en) 1/0 The point coinciding in the deformed condition with $1,111 will lie at mz=u+en xo Continuing in this way a plurality of points can be determined with the general coordinates which points must all lie on the curve to be determined. If from the last equations the parameter n is eliminated then it appears that the co- This Equation (A) is derived as follows:-

Taking as a starting point xn=(1+er)$o this may also be put down as follows:

In the same way it is possible to derive from ya 1) "Ya ya 1g n+6.) It is possible therefore either to put down:

Since from the last equation the parameter n has been eliminated, this equation is valid not only for the points xn, Z/n, but also for any other points x, y; it is therefore possible to put down the equation also in this form:

However, it appears also that any arbitrary point of the curve represented by this equation will again reach said curve due to the deformation under the load 10, q. Such a point x, 1/ namely is transferred to which coordinates indeed satisfy the Equation A for the curve, since substitution results in or, in connection with the Equation A (1 01K -l n) (1 E018 r) which is indeed an equality.

All the points of a meridian curve 2 therefore in the case of a deformation corresponding to the load p, q will lie again on the curve 2.

It should still be made acceptable that if the pressures p and q have each attained a predetermined fraction, only (up and aq) of their final value the meridian curve of the deformed body is still represented by the Equation A, since it is an' object of the invention to determine the meridian curve of the matrix so that when relieving the pressure p the matrix permits the compressed mass to expand in such a manner that the pressure q decreases proportionally. To this end it should be proved that with pressure up and uq (0 a 1), to which specific strains men and w correspond, the equation of the corresponding curve also if Ea (the largest of the two ductile stresses) has the high value 1/10, 63, will only have the 30 value 1 100. Therefore there are no objections to write 1g (1 11s,) ore,-

35 so that the Equations A and B respectively may be written:

40 from which it appears that the curves represented by said equations (apart from the slight values neglected) are identical, so that with a matrix according to the invention the purpose aimed at can indeed be attained, i. e. to press briquettes or tablets from powderlike and granular substances, which after the relief of the compression-pressure do not break up, by means of a press of exceedingly simple construction. It is obvious that in selecting the material and the machining of the mold care is to be taken that the coefficient of friction of the said material with regard to the material to be compressed is such that the said coefiicient of friction will produce a shearing stress 1' at the surface of the briquette which will satisfy the value theoretically required for the same, i. e. that the said shearing stress for every point of the surface of the briquette will equal, or practically equal in which represents the angle formed by the tangent drawn at the said point of the surface of the briquette and a horizontal line. It is obvious that in practical making of such a pressing mold for constructing the meridian curve of the pressing mold a graphic approximation may be applied.

I claim:

A pressing mold for the manufacture of briquettes from fine grained materials, materials in powder form, and the like, characterized in that the interior wall of the said mold is formed by the bounding surface of a solid of revolution, the generatrix of which surface satisfies the equawith respect to a coordinate system the y-axis of which coincides with the axis of rotation.

WILLEM BOLK.

sin 2 

